This highly original and challenging study offers an examination of the tensions which exist between the two most important sources of international law: Treaty and Custom. Through detailed analysis of state practice and key decisions of international tribunals, the author considers the circumstances by which new customary law may abrogate the obligations of a prior treaty, and argues that there is a special category of situations which supports the right of a state to renegotiate a treaty by an appeal to new customary law. Scholarly and thought-provoking, this is an original and, at times,...